Baxi Combi Instant 105 HE fault?

Hi, on the above boiler we had a PCB fitted to replace a fault (Demestic hot water mode). This produced a flashing neon no 6 Flame failure / or blocked Condensate Drain. On re-setting the boiler we now have no neons except power on. No hot water or heating. I have just ordered an air presure switch at £20. Trying the cheap options first. Heating engineer returning tommorow. Has anyone got any suggestions? Thanks in advance. Dave